U -
Interface - The interface between the ISDN BRI line and the NT1. This can be
considered the ISDN "phone jack" in the USA & Canada and is
frequently in the form of a RJ-11 or RJ-45 type telephone jack.

U/C -
upconverter

U/L -
uplink

UA - user
agent

UAN -
universal area network

UART -
universal asynchronous receiver/transmitter

UAV -
unmanned aerial vehicle

UBR -
unspecified bit rate

UBS -
unclassified but sensitive

UCAV -
uninhabited combat aerial vehicles

UCCS -
(EUCOM) command and control system

UCMJ -
Uniform Code of Military Justice

UCNI -
unclassified controlled nuclear information

UCSB -
Universal Clock Synchronizer Board

UDDI -
universal description discovery and integration

UDF - user
defined functions

UDP - User
Datagram Protocol

UFC -
universal feature card

UFO -
ultra-high frequency follow-on satellite

UHF -
ultra high frequency

UI - user
interface

UIDL -
user interface definition language

UIMS -
user interface management system

UIRV -
Unique Interswitch Rekey Variable

UISRM -
user interface system reference model

UITC -
user interface transit case

UJTL -
Uniform Joint Task List

ULANA -
unified local area network architecture

ULCS -
Unit Level Circuit Switch

ULF -
ultra low frequency

ULMS -
unit level message switch

ULP - ultra
low power

ULP -
upper layer protocol

ULS - user
location server

ULSI -
ultra-large-scale integration

UM -
universal modem

UMC -
(Unassigned Multiplex Channel Code) - This NCC is transmitted for a DS0B
channel that is not active.

UML -
universal modeling language

UMS -
universal modem system

UMTS -
universal mobile telecommunications system (Europe)

UNE -
unbundled number elements

UNI -
user-network interface

Unipolar -
Unipolar (of one polarity) is the fundamental characteristic of internal
signals in digital communications equipment. A unipolar signal represents
simply, one of two states: on or off; 1 or 0. A unipolar signal may either: go
on for the portion of the bit time, and then return to zero state (unipolar
RZ); or, go on (and stay on) as long as consecutive one bits are present, not
returning to zero until a zero state occurs (unipolar NRZ). Contrast with
bipolar.

UNO -
universal networked object

UOES -
user operational evaluation system

UPS -
uninterruptible power supply

UPT -
universal personal telecommunications

URAV -
uninhabited reconnaissance aerial vehicles

URG -
urgent pointer flag, TCP header

URL -
uniform (universal) resource locator

US -
ultraspectral sensor

US - user

US -
United States

USA -
United States Army

USACC -
U.S. Army Communications Command

USAF -
United States Air Force

USAFE -
United States Air Forces in Europe

USAISC -
US Army Information Systems Command

USAISSAA -
US Army Information Systems Selection and Acquisition Agency

USAR -
United States Army Reserve

USARPAC -
US Army Pacific

USARSO -
United States Army Forces Southern Command

USASOC -
United States Army Special Operations Command

USAT -
ultra small aperture terminal

USB -
universal serial bus

USB -
upper sideband

USCENTCOM
- United States Central Command

USCG -
United States Coast Guard

USCINCCENT
- Commander in Chief, US Central Command

USCINCEUR
- US Commander in Chief, Europe

USCINCJFCOM
- Commander in Chief, US Joint Forces Command

USCINCPAC
- Commander in Chief, US Pacific Command

USCINCSO -
Commander in Chief, US Southern Command

USCINCSOC
- Commander in Chief, US Special Operations Command

USCINCSPACE
- Commander in Chief, US Space Command

USD -
(Universal Synchronous Data) Module - This module provides two independent
synchronous data ports with V.35 or RS-449/422 DCE/DTE interfaces at rates from
1.2 kbps to 1.344 Mbps and RS-232 DCE/DTE interfaces at rates from 1.2 kbps to
19.2 kbps. Also supported is a RS-530 DCE interface at rates of 1.2 kbps to
1.344 Mbps.